There are known viscous or viscoelastic agents for ophthalmic surgical use, for example, Viscoat.RTM. (Alcon Surgical, Inc.) which contains the viscoelastics, sodium hyaluronate and chondroitin sulfate; Healon.RTM. and Healon GV (Kabi Pharmacia), Amvisc Regular and Amvisc Plus (IOLAB), and Vitrax (Allergan) which contain sodium hyaluronate; Orcolon (Optical Radiation Corporation) which contains a polyacrylamide; and Occucoat (Storz) which contains hydroxypropylmethylcellulose (HPMC). All of these products are useful in cataract surgery. They are used by the skilled ophthalmic surgeon for several purposes, maintenance of the anterior chamber of the eye and protection of ophthalmic tissues during surgery, particularly corneal endothelial cells, and as an aid in manipulating ophthalmic tissues.
While all of the products described above may be used during cataract surgery, there is no one product, or viscous or viscoelastic agent (hereinafter "agent") which best fulfills all of the purposes. All have their own advantages and disadvantages. For example, Viscoat.RTM. works extremely well in maintaining the anterior chamber during capsulotomoy, or anytime during the cataract procedure, and in adhering to and protecting tissues, particularly the corneal endothelium. But, Viscoat.RTM., due to its adhering and coating characteristics is relatively difficult to remove from the anterior chamber of the eye. In addition, although it can be used to manipulate tissue for insertion of an intraocular lens into the eye, other agents are known to work better for this purpose.
Pure sodium hyaluronate products can be very useful in manipulating tissues during surgery, for example, it can be used to inflate the capsular bag to facilitate the insertion of an intraocular lens (IOL). However, sodium hyaluronate is not as effective as some agents in maintaining the anterior chamber and protecting ophthalmic tissues. Because it is highly cohesive, and thus very useful in manipulation, it is not as effective in adhering to, and protecting tissues. Its cohesiveness also makes it easier to remove from the eye at the end of surgery.
HPMC adheres well to ophthalmic tissues and therefore protects them, but is not as good as, for example, Viscoat.RTM., in maintaining the anterior chamber, or as good as sodium hyaluronate in manipulating tissues. However, it can be easily diluted with irrigation fluid following IOL implantation. This helps prevent intraocular pressure spikes following surgery.
In general, products containing relatively higher molecular weights of sodium hyaluronate are more effective in maintaining the anterior chamber and protecting tissues than relatively lower molecular weight sodium hyaluronate products; however, they tend to be highly cohesive and may be prematurely aspirated from a surgical site. Products, which due to their tenacious characteristics adhere to and protect tissues, are more difficult to remove from the surgical site.
It would be advantageous to use more than one agent during an ophthalmic procedure, such as a cataract operation, to obtain the maximum benefits offered by the variety of available viscoelastic agents. The methods of the present invention provide this advantage.